Diagnosing MTA Problems using Telnet
1.The most common way to identify and track remote SMTP mail server problems is actually with Telnet: not Telnet as in a shell or login to the server, but running Telnet to the SMTP port (port 25) on the mail server itself and attempting to send a message directly to the server using the SMTP protocol.
2.The resulting output will show you exactly what happens when a message is delivered on your machine, and is a good way to diagnose server issues, rule out or prove user/client-side issues, or identify things such as problems with SMTP-Auth.
This command session shows you how:
# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^ ]'.
220 playground.test.mydomain.com ESMTP Sendmail 8.11.6/8.11.6;
Tue, 10 Sep 2002
14:11:41 -0500
ehlo mydomain.com <---------------Initial Handshake & Option Listing 250-playground.test.mydomain.com Hello localhost [127.0.0.1], pleased to meet you 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-SIZE 250-DSN 250-ONEX 250-ETRN 250-XUSR 250-AUTH LOGIN PLAIN <------------------- Types of SMTP-Auth 250 HELP mail from:tweeks@mydomain.com <------------Email "From" 250 2.1.0 tweeks@mydomain.com... Sender ok rcpt to:tweeks@mydomain.com <------------- Email "To" 250 2.1.5 tweeks@mydomain.com... Recipient ok data <------------------------------------ Go into "data mode" 354 Enter mail, end with "." on a line by itself SUBJECT: This is a test from Playground This is a test.. Tweeks . <-------------------------------------- Terminating "." 250 2.0.0 g8AJBu004136 Message accepted for delivery quit <------------------------------------ 221 2.0.0 playground.test.mydomain.com closing connection Connection closed by foreign host.
1.The most common way to identify and track remote SMTP mail server problems is actually with Telnet: not Telnet as in a shell or login to the server, but running Telnet to the SMTP port (port 25) on the mail server itself and attempting to send a message directly to the server using the SMTP protocol.
2.The resulting output will show you exactly what happens when a message is delivered on your machine, and is a good way to diagnose server issues, rule out or prove user/client-side issues, or identify things such as problems with SMTP-Auth.
This command session shows you how:
# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^ ]'.
220 playground.test.mydomain.com ESMTP Sendmail 8.11.6/8.11.6;
Tue, 10 Sep 2002
14:11:41 -0500
ehlo mydomain.com <---------------Initial Handshake & Option Listing 250-playground.test.mydomain.com Hello localhost [127.0.0.1], pleased to meet you 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-SIZE 250-DSN 250-ONEX 250-ETRN 250-XUSR 250-AUTH LOGIN PLAIN <------------------- Types of SMTP-Auth 250 HELP mail from:tweeks@mydomain.com <------------Email "From" 250 2.1.0 tweeks@mydomain.com... Sender ok rcpt to:tweeks@mydomain.com <------------- Email "To" 250 2.1.5 tweeks@mydomain.com... Recipient ok data <------------------------------------ Go into "data mode" 354 Enter mail, end with "." on a line by itself SUBJECT: This is a test from Playground This is a test.. Tweeks . <-------------------------------------- Terminating "." 250 2.0.0 g8AJBu004136 Message accepted for delivery quit <------------------------------------ 221 2.0.0 playground.test.mydomain.com closing connection Connection closed by foreign host.
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